The role of cerebral noradrenergic systems in the Fos response to interleukin-1

Peripheral administration of interleukin-1 (IL-1) has been shown to activate induction of Fos in the brain, but the mechanism is not known. Because cerebral noradrenergic systems have been implicated in Fos induction, we studied the IL-1-induced appearance of Fos in mice pretreated with 6-hydroxydopamine (6-OHDA) which depleted cerebral norepinephrine (NE) by more than 90%, but did not significantly alter dopamine. Intraperitoneally injected IL-1β increased Fos in several brain regions, but most obviously in the hypothalamic paraventricular nucleus (PVN). Pretreatment with 6-OHDA substantially reduced the IL-1-induced Fos increase in the PVN which was no longer statistically significant. When the 6-OHDA treatment was preceded by administration of desmethylimipramine which prevents NE depletion, IL-1 treatment increased Fos in the PVN, suggesting that the effect of 6-OHDA was indeed related to the depletion of NE. These results suggest that the noradrenergic innervation of the PVN is involved in the IL-1-induced induction of Fos in the PVN. By contrast with previous experiments in rats, the IL-1-induced increase in plasma corticosterone was not significantly altered by the 6-OHDA pretreatment in mice.